I have been reading a good deal about IMC (purple plague in particular) in gold wire/aluminum pad wire bonds. My company uses ultrasonic wedge bonding, and for the most part all of our bonding is gold/gold, however we have one particulr part that has several customer-supplied aluminum pad chips. Of all of our products, this particular product has the highest failure rate at test (almost all failures are no communications from the chips), and I was wondering if anybody has any experience dealing with Au/Al bonding problems? My biggest question is if the underfill and encapsulant heating and curing cycles (3 total after the bonding) could be creating IMC issues that could cause high rates of failures. Thanks for your help! -Ryan

Well, I can't speak for them falling off later on, as that's not when I see them, and they are passing their wire pull tests after bonding. What I am seeing is electrical opens during testing, and these opens coincide with the Au/Al bonded points. That's why I am wondering if there is an electrical open, not a physical open, which is what started me thinking that the problem could be IMC at the bond. Since the wire pulls are performed prior to the encapsulant and heating cycles, it's difficult to see if there is a problem developing after the fact